The present invention is directed to a method for producing lamented embossed webs and more particularly to a method of applying adhesive to at least one of the embossed webs and an application unit for applying such adhesive.
Multiple ply lamented embossed paper products are typically of two types, xe2x80x9cnestedxe2x80x9d and xe2x80x9cpillowedxe2x80x9d, each of which have substantially greater bulk than non-embossed multiple ply products. When a tissue or towel sheet is provided with an embossed pattern, projecting raised areas and recessed areas are produced corresponding to the protuberances and recessed areas of the embossing rolls. A xe2x80x9cnestedxe2x80x9d product results when projecting raised areas of a first web are aligned with the recessed areas between two raised areas of a second web, whereas a xe2x80x9cpillowedxe2x80x9d sheet results when projecting raised areas of both first and second webs are placed adjacent one another with the recessed areas of the two sheets creating a relatively large void between adjacent raised areas.
The primary problem associated with multi-ply embossed paper webs is that, traditionally, the plies have been combined at the nip between the steel embossing rolls. This metal-to-metal contact at the embossing roll nip has resulted in excess wear of the embossing rolls requiring frequent and costly repair or replacement of the rolls. This problem was recognized in U.S. Pat. No. 3,867,225 issued to Nystrand wherein the plies are combined between one of the steel embossing rolls and a rubber-covered xe2x80x9cmarrying rollxe2x80x9d which permits the nip between the two embossing rolls to be run open, thereby reducing wear on and extending greatly the useful life of the embossing rolls.
However, the process set forth in the above-noted patent to Nystrand, is useful only for producing a xe2x80x9cnestedxe2x80x9d type product since the solid surface marrying roll would substantially debulk a pillowed product. A pillowed multi-ply product is shown in U.S. Pat. No. 3,738,905 issued to Thomas, however, this method suffers from the aforementioned embossing roll wear problem at the combiner nip. A solid surface marrying roll, as disclosed in the Nystrand patent utilized with this process would result in approximately fifty percent of the lamented bulk sheet being removed during the embossing stage.
In an effort to overcome the aforementioned shortcomings, a relief pattern marrying roll is set forth in U.S. Pat. No. 4,483,728 issued to Bauernfeind wherein a marrying roll especially adapted to combine multiple plies of a tissue sheet at a nip between the marrying roll and an embossing roll is set forth. The marrying roll is provided with a pattern of raised lamented elements covering a predetermined percentage of the marrying roll surface which are caused to bear against the raised embossing elements of an embossing roll with the plies of a pillowed tissue sheet therebetween. The pattern of raised elements on the marrying roll surface may be in the form of dots, a rectangular grid pattern, or any other pattern of choice. The pattern is preferably aligned at an angle to the machine direction to eliminate bunching or puckering of the tissue sheet between pattern elements. During the manufacture of the multi-ply web, adhesive is applied to the projecting raised areas of one of the plies; however, the embossed webs are related with one another but not joined at an open nip between the embossing rollers in that the adhesive which has been applied is insufficient to laminate the webs together because the nip between the embossing rolls is run in the open position to prevent embossing roll damage often experienced in such systems. It is the marrying roll which presses the plies together to adhered such plies to one another which forms the two-ply web. In this regard, the embossing rolls are inadequate to adhere the single ply webs to one another and the use of marrying roll results in a decrease in the lamented sheet bulk.
U.S. Pat. No. 5,215,617 issued to Grupe sets forth yet another method of forming multi-ply webs wherein matched rubber and embossing rolls are used to reduce strength degradation of the ply during embossing and to permit the use of rotogravure adhesive printing when forming nested webs. That is, matched embossing roll pairs are used to emboss separate paper plies which are subsequently adhered to one another by adjacent rolls of each of the pair of embossing rolls. When forming the nested ply, one of the embossing rolls includes a rubber covered roll having embossing elements which permits the use of rotogravure adhesive printing. However, this reference fails to recognize the formation of a pillow type multi-ply web wherein the plies are adhered to one another at the nip formed between adjacent embossing rolls. Further, applying the adhesive to the raised portions of the soft rubber roll may result in a reduction in the effectiveness of the spot bonding between plies which results in stiffening of the two-ply web.
Additionally, the aforementioned methods of forming multi-ply webs utilize adhesive application units which merely apply a layer of adhesive material to the outermost extended portions of the web as such web bypasses the adhesive applicator. This type of adhesive application often results in adhesive build up on not only the applicator but also, and more importantly, on the back-up roller carrying the web to which the adhesive is being applied. This occurs due to the porous nature of the web material which allows a portion of the adhesive material to bleed through the web and accumulate on the back-up roll. Because the adhesive is continuously applied to the portion of the web which overlies the same portions of the back-up roll, the adhesive accumulates on the back-up roll wherein over time, continued operation of the back-up roll eventually requires that the device be shut down and the back-up roll cleaned periodically to ensure proper lamination of the webs together in the nip region of the device. This shutdown results in higher operating costs and a reduction in the output capacity of the device translates into lost revenues for the manufacturer.
Therefore, there is a need for an embossing roll arrangement which will permit the embossing of pillowed type multi-ply webs without debulking the web in any manner. Further, there is the need for a method of producing a multi-ply soft absorbent web while eliminating the use of a marrying roll which inherently reduces the overall bulk of the multi-ply web. Moreover, there is a need for a method of forming pillow type multiply webs having equal emboss definition on both sides thereof and which is not unduly stiffened by the application of adhesives. Moreover, there is a need for an adhesive application unit for selectively applying adhesive to an embossed web in a manner which permits the back-up roll carrying the web to clean itself between applications to reduce the amount of adhesive build-up on the rolls and to limit the amount of adhesive applied to the web itself so as to not unduly stiffen the web.
A primary object of the present invention is to overcome the aforementioned shortcomings associated with the prior art methods discussed hereinabove.
A further object of the present invention is to provide a method for forming a pillow type multi-ply web having equal emboss definition on both sides.
Yet another object of the present invention is to provide a method of forming a pillow type multi-ply web wherein the bulk density of the web is not destroyed by the adhesion of the webs to one another.
A further object of the present invention is to provide a method of forming a multi-ply web wherein the bulk density and definition of the web is enhanced.
Yet another object of the present invention is to provide a multi-ply web wherein sheets stiffness due to the adhesion of the webs to one another is reduced.
A still further object of the present invention is to provide a multi-ply web wherein the sheets of the multi-ply web are selectively adhered to one another so as to limit the application of adhesive to the plies so as to not unduly stiffen the multi-ply web.
These, as well as additional objects of the present invention, are achieved by forming a multi-ply web by embossing a first ply between a first pair of matched embossing rolls including a first embossing roll having protuberances formed in a substantially rigid outer surface and a second embossing roll having protuberances formed of a resilient material thereby forming raised portions and recessed portions in the first ply, embossing a second ply between a second pair of matched embossing rolls including a third roll have protuberances formed in an outer surface formed of a resilient material and a fourth roll having protuberances formed in a substantially rigid outer surface thereby forming raised portions and recessed portions in the second ply with the first and second pairs of matched embossing rolls being positioned such that the first embossing roll is positioned adjacent the third embossing roll forming a nip region between the protuberances formed in each roll. An adhesive is applied to the web carried by the first roll with the first ply and second ply being adhered to one another in the nip region wherein the raised portions of the first and second plies are adhered to one another and the recessed portions of the first and second plies are spaced from one another. Such a multi-ply web may also be formed by separately embossing first and second plies with a pattern of raised portions and recessed portions, applying adhesive to at least some of the raised portions of one of the first and second plies and passing each of the plies through a nip formed between a first roll having a resilient outer surface and a second roll having a substantially rigid outer surface wherein the raised portions of the first and second plies are adhered to one another and the recessed portions of the first and second plies are spaced from one another.
Alternatively, the above noted advantages may be achieved by forming a multi-ply web by embossing a first ply between a first pair of matched embossing rolls including a first embossing roll having protuberances formed in a substantially rigid outer surface and a second embossing roll having protuberances formed of a resilient material thereby forming raised portions and recessed portions in the first ply, embossing a second ply between a second pair of matched embossing rolls including a third roll have protuberances formed in an outer surface formed of a resilient material and a fourth roll having protuberances formed in a substantially rigid outer surface thereby forming raised portions and recessed portions in the second ply with the first and second pairs of matched embossing rolls being positioned such that the second embossing roll is positioned adjacent the third embossing roll forming a nip region between the protuberances formed in each roll. An adhesive is applied to the web carried by the first roll with the first ply and second ply being adhered to one another in the nip region wherein the raised portions of the first and second plies are adhered to one another and the recessed portions of the first and second plies are spaced from one another.
Further, in order to decrease the stiffness of the multi-ply web, adhesive is preferably be applied by way of a printing plate and reverse enclosed doctor blade so as to apply the adhesive in selected locations on the web thereby minimizing the amount of adhesive applied to the web. In doing so, the amount of adhesive build up on the embossing rolls, due to the adhesive bleeding through the web material is minimized and the embossing rolls are permitted to clean themselves in that the adhesive application is carried out so that adhesive is not applied to the web material adjacent portions of the embossing roll on successive rotations of the roll. By doing so, portions of the backup roll which support the web where adhesive was previously applied are permitted to self clean by allowing the adhesive which has bled through the web and collected on the backup roll to dry and flake off prior to adhesive again being applied to the web adjacent such region.
These, as well as additional advantages of the present invention will become apparent from the following detailed description of the invention when read in light of the several figures.